1. Field of the Invention
The present invention relates to a semiconductor device, and more specifically to a SON (Silicon-On-Nothing) MOSFET having a beam structure and an inverter that uses the SON MOSFET as well as a method for fabricating the SON MOSFETs and the inverter so as to increase the performance and efficiency of the MOSFET.
2. Description of the Background Art
Recently, one chip technology has been rapidly developed to integrate multiple semiconductor devices.
In particular, as the integration intensity of the MOSFET has increased and the size of MOSFETs has decreased, the potential barrier of the MOSFET's gate and drain has decreased, because a lateral electric field due to a drain voltage becomes relatively larger than a vertical electric field due to a gate voltage. It makes the effective channel length of the MOSFET become shorter than that of MOSFETs having long channel length. This phenomenon causes heavy coupling of the gate voltage and the drain voltage (known as a Short Channel Effect).
This Short Channel Effect makes device characteristics worse. Moreover, off-current of the MOSFET tends to increase due to this Short Channel Effect.
To solve these problems, various methods like SOI (Silicon-On-Insulator) and SON (Silicon-On-Nothing) MOSFETs have been introduced. For the SOI type, the MOSFET is electrically insulated from the bulk by making it on a SOI wafer which uses a SiO2 layer to insulate top silicon and bottom silicon wafers. The SON type has been implemented by forming a cavity by selectively implanting nitrogen into a predetermined region of the semiconductor substrate or by forming an air cavity through lateral etching on the side of the gate.
However, the conventional SOT and SON MOSFETs have some problems. That is, the price of a SOI wafer is much higher than that of a normal wafer, and the performance of the SOI MOSFET is lower than that of MOSFETs using the SON structure. For SON type MOSFETs, it is not suitable for mass production because the fabrication process is so complex and high level accuracy in alignment is required to form each electrode.